POU4F2 and retina neoplasm: The 661W cells derived from mouse retinal tumors positively express cone marker Opn1mw; RGC markers such as RBPMS, BRN3b (Pou4f2), BRN3c (Pou4f3), Thy1, and γ-synuclein (Sncg); and some other neuronal markers (β-III Tubulin, NeuN, and MAP2) [28]; however, ARPE-19 cells derived from the human pigment epithelium, expressing the specific pigment epithelium CRALBP and RPE65, shows distinct differences in origin and growth features from 661W cells [29].